Energy Transfer

1
Energy Transfer

• 10.2

2
Energy Transfer

• Energy is transferred from hotter object to
  colder object
• Examples?
• Cooking pasta
• Making ice
• Making popcorn
• Roasting marshmallows

3
Three Methods of Energy Transfer

• Conduction
• Convection
• Radiation

4
Conduction

• Transfer E as heat between particles in direct
  contact
• Example
• Roasting marshmallow with wire
• Air molecules collide with wire
• Transfer energy to wire
• Particles in wire move faster, have more E
• E then transfer to hand, detect warmth

5
Convection

• Energy transfer through movement of fluids at
  different temperatures (fluids - liquids and
  gases)
• Examples
• Camp fire
• See soot, embers rise swirl
• Rise upwards warm air expands
• Why?

6
Convection

• Convection current flow of fluid due to heated
  expansion followed by cooling and contraction
• Examples
• Fire, candle
• Warm air rises, cools, then flows downward
• See p. 332, fig 10-8
• Wind current
• Boil water in pot

7
Convection

• You can hold your fingers beside the candle flame
  without harm, but not above the flame. Why?

8
Radiation

• Transfer of E by electromagnetic waves
• No movement of matter will work in vacuum or
  outer space
• No contact or movement of fluid
• Infrared, visible light, UV rays
• Example
• Fire emits radiation (infrared), skin absorbs E,
  increase in temperature

9
Radiation

• Radiation can be absorbed and emitted
• Color
• Summer day wear light or dark clothes?
• Winter day wear light or dark clothes?
• Why?

10
Radiation Lab

• Suppose we fill a black soup can and a silver
  soup can with the same amount of water.
• If we put them both under the same light bulb,
  which one would reach a higher temperature?
• If we turn off the light source after 30 minutes,
  which one would cool off faster?

11
Radiation Lab

• Lets find out!
• Make a data table with the time, temperature of
  black can, and temperature of silver can.
• Well take the temperature every 5 minutes.